Hydrocyanation of butadiene to form pentenenitrile (PN) is known in the art, e.g., U.S. Pat. No. 3,766,237. The predominant pentenenitriles so formed, e.g., 3-pentenenitrile, 4-pentenenitrile and 2-methyl-3-butenenitrile, are further subjected to hydrocyanation and/or isomerization to form adiponitrile (ADN), a commercially important material in the synthesis of nylon.
In the liquid phase, 2-methyl-3-butenenitrile can be efficiently isomerized to 3- and/or 4-pentenenitrile, in the presence of zero-valent nickel catalysts, which products are easily further hydrocyanated to form adiponitrile. No such techniques for carrying out this isomerization in the gas phase are known. A related study by Kurokawa et al., (Journal of Catalysis, 141, 94-101 (1993)) describes the gas phase isomerization of 3-pentenenitrile to a mixture of branched and linear pentenenitriles. Catalysts used include SiO.sub.2, MgO or CaO, at temperatures of 350.degree. C. and 370.degree. C. Ratios of branched to linear products in the range of 19/35, 24/18 and 10/49 were reported. In all cases, only conjugated branched compounds were obtained; that is, no 2-methyl-3-butenenitrile was formed.